A ripple having a frequency twice a power source frequency is present in power obtained from a single-phase AC power source. Thus, when a DC voltage is obtained by rectifying a single-phase AC voltage obtained from the single-phase AC power source, a large-capacitance energy accumulation element is necessary to make this DC voltage constant.
In view of such a necessity, there has been proposed a technique that adopts a power buffer circuit in which a buffer capacitor is connected to a DC link via a switching element, thereby forming a voltage source (for example, Japanese Patent No. 580416 and Yamashita and Sakakibara, “A. Control Method of a Single-phase-to-three-phase Power Converter with an Active Buffer for Increasing Voltage Transfer Ratio”, IEEJ Transactions on Industry Applications, Vol. 137, No. 2. The Institute of Electrical Engineers of Japan, Feb. 1, 2017, pp. 112-118 listed below). According to such a technique, the voltage source allows a current input to a direct power converter that forms a high-frequency link as well as a voltage obtained from a single-phase AC power source to have a waveform of a sinusoidal wave, implementing high-efficiency characteristics.
The technique described above enables a DC voltage of the DC link to be increased to a crest value of the single-phase AC voltage (for example, Yamashita and Sakakibara, “A Control Method of a Single-phase-to-three-phase Power Converter with an Active Buffer for Increasing Voltage Transfer Ratio”, IEEJ Transactions on Industry Applications, Vol. 137, No. 2, The Institute of Electrical Engineers of Japan, Feb. 1, 2017, pp. 112-118). However, when a practical value, for example, a value that is 1.17 times the crest value, is selected as a buffer voltage allotted to the buffer capacitor, a voltage utilization ratio is only approximately 0.87. On the other hand, there has been proposed a control method that improves the voltage utilization ratio to 0.95 for the same buffer voltage (for example, Japanese Patent No. 5930108 listed below).
Unlike the above-described control methods based on a magnitude of power provided to and received from the power buffer circuit, a control method focused on a voltage output from a power converter has also been proposed (for example, Japanese Patent No. 5626435 and Yamashita and Sakakibara. “A Control Method of a Single-phase-to-three-phase Power Converter with an Active Buffer for Increasing Voltage Transfer Ratio”, IEEJ Transactions on industry Applications, Vol. 137, No. 2, The Institute of Electrical Engineers of Japan, Feb. 1, 2017, pp. 112-118). This control method implements a boosting operation by increasing a ratio of steady-state power to power allotted to the power buffer circuit (power provided to or received from the DC link). Such a control method is effective in a voltage range in which the allotted power does not increase greatly.
In addition, examples that disclose a technique for controlling an amplitude of an input current on the basis of a buffer voltage include Japanese Patent No. 5874800.